When I encountered this bug, I had success with the following method :

1) Completely reset wireless router (Linksys WRT54G), essentially killing the current WLAN. *Note: This is different from rebooting the router. Rebooting did NOT work in my case.*
2) Access router through router's IP address and reconstruct network from scratch (actually a fairly quick process).
3) Reconfigure network settings on each computer (also pretty quick), reflecting changes to new WLAN.
4) Check settings on N800 to be certain that the weps, etc. are current.

In short, I scrapped my network and started from scratch. I'm not sure why, but it worked like a charm.

Best of luck~
Octarine